This invention relates to electrical leads, and more particularly to a lead which connects a source of electrical signals to an organ of the body such as the heart.
It is known to stimulate internal body organs such as the heart with electrical signals generated by an electronic device such as a pacemaker. These signals compensate for various cardiac dysfunctions such as rhythm disorders. Generally, the pacing device itself is located some distance away from the organ needing stimulation and is connected to the organ by an electrical lead.
One way of establishing electrode contact with heart muscle is to feed the electrode and its lead through the venous system into the heart. It is necessary in this case that the lead somehow be imparted with sufficient stiffness and maneuverability to negotiate the various turns encountered in the journey through the venous system to the heart. Once installed, the lead must have sufficient flexibility to withstand the continuous motion of the body over many years without undue mechanical stress. It is also desirable that a stimulating lead have small diameter to lessen interference with blood flow, to facilitate introduction into the vascular system and to accommodate multiple lead systems.
In the prior art, it is known to employ a lead with a central hole or lumen inside a long hollow coil of electrically conductive wire. A relatively stiff guide wire or stylet is inserted into the lumen as an aid for feeding the lead through the venous system. The stylet is fed through the lead all the way until it encounters the closed distal end of the lead. As the physician continues to push the proximal end of the stylet, the stylet transmits axial force to the electrode end of the lead. The lead in turn is driven, or actually pulled forward from the distal end. Observing the position of the end of the lead on a fluoroscope during the procedure, the physician quickly "threads" the lead through the vascular system by manipulating the stylet from the outside. Physicians specializing in implantation of cardiac pacers, for example, are used to the foregoing procedure and have highly developed skills which enhance confidence in the procedure. The ease and familarity of the stylet procedure also help reduce the trauma to the patient while insuring positive placement of the lead. Once the lead is installed, the stylet is removed. The remaining overall lead diameter, of course, is larger than would have been the case without the stylet-receiving lumen.
The electrodes on the distal ends of prior art cardiac stimulating leads are frequently equipped with protruding tines or fins to aid in attachment to the inside wall of the heart. These prior art electrodes were of relatively large diameter requiring a large diameter introducer sheath for entry into the vascular system. In addition, the need to restrict the overall diameter of the electrode required that the fins be kept small. Small fins, however, provide insufficient "anchoring".
It is, therefore, an object of the present invention to provide an extremely flexible stimulating lead with a reduced diameter while preserving stylet-like action during the implantation procedure.
It is a further object of the present invention to provide a lead having a distal tip of smaller diameter and longer fins without unduly increasing the overall diameter of the lead during introduction into the vascular system.